Cathode ray tube structure including combined electrostatic and magnetic convergence system



2,907,915 E INCLUDING COMBINED ELECTROSTATIC AND MAGNETIC CCNVERGENCE SYSTEM Oct. 6, 1959 P. H. GLEICHAUF CATHODE RAY TUBE STRUCTUR Filed Feb. 16, 1956 INVENTOR PAUL H. GLEICHAUF1 2,907,915 Patented Oct. 6, 1959 cArHoDE RAY TUBE STRUCTURE INCLUDING COMBINED ELEcTRosrATrC AND MAGNETIC coNvERGENcE SYSTEM Paul H. Gleichauf, Syracuse, N.Y., assigner to General Electric Company, a corporation of New York Application February 16, 1956, Serial No. 565,859

7 Claims. (Cl. '315-13) My invention relates to cathode ray tubes and pertains more particularly to a new and improved cathode ray tube struc-ture including improved means adapted for effecting convergence' of electron beam: components therein.

Colo-r cathode ray tubes to Which the present invention is particularly applicable generally include a luminescent :screen comprising part of a target electrode in which different phosphor areas produce differently colored light when excited by electron beam components impinging thereupon, means for producing and directing a plurality of electron beam components toward the target electrode and means for deflecting the beam cornponents thereby to -scan a raster at the target electrode. In such tubes it is generally necessary to provide means for effecting substantial convergence kof the different elec- -tron beam components at all points of the raster scanned thereby at the :target electrode. Heretofore, various means have been resorted to in an attempt to accomplish satisfactory beam convergence. However, they have been found generally unsatisfactory in that they resulted in complicated Iand ex-pensive :tube constructions, required considerable complicated control equipment, or effected undesirable distortion of the beam components with resultant color impurities. Accordingly, the primary object of the present invention is to provide a new and improved color cathode ray tube structure.

Another object of the present invention is to provide a new and improved color cathode ray tube structure including new and improved means adapted for effecting convergence of beam components at rall points of a raster scanned by such components. K

Another object of -the present invention is to provide a new and improved arrangement adapted for effecting both static and dynamic beam convergence.

Another object of the present invention is to provide a new and improved color cathode ray tube including a single convergence system adapted for both electrostatic and magnetic convergence control of electron beam components therein.

Still another objectof the presen-t invention is to provide a new and improved beam-convergence arrangement which is Asimple and less expensive in construction, provides improved color quality and is controllable without the complicated control equipment heretofore required.

Further objects and advantages of my invention will become apparent as the following description proceeds and the fea-tures of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of my invention, I provide a cathode ray tube -including 1a target electrode, means for producing and directing several substantially co-v planar electron beam components toward the targetelectrode and means for deflecting the components to effect scanning thereof at -the target electrode. Also included in the tubey structure and straddling outer components are pairs of elements adapted for electrostatically deflecting and thus converging the louter beam components on a plane of deflection determined by an inner beam cornponent.V These elements lare further adapted to serve as internal magnetic pole pieces adapted for having magnetic fields established therebetween thereby magnetically to deflect and thus effect convergence of the electron beam components in a plane perpendicular to the one determined by the inner component.,- Magnetic field producing means located externally of the tube are adapted for being energized to effect both a static magnetic convergence of the beam components and a dyv namic magnetic convergence in accordance with the raster positions of the scanning components.

For a better understanding of my invention, reference may be had to the accompanying drawing in which:

Figure l is a schematic fragmentary illustration of a preferred form of the present invention; and

Figure 2 is a sectional view taken along the line 2 2 in Figure 1 and looking in the direction of the arrows.

Referring to Figure l, there is shown a color cathode ray tube structure generally designated 1 including an envelope 2 having a cylindrical neck portion 3, a transparent viewing end or face plate portion 4 and a substantially yconical transitional portion 5.

Located at the viewingend of the envelope 2 is a target electrode generally designated 6. The target electrode 6 includes a phosphorescent material coating or screen 7. The screen 7 is supported on the inner surfacer of the face plate portion 4 and preferably comprises phosphors capable of producing light of different colors in response to4 any impingement thereon by charged particles or electrons. The screen 7 preferably comprises red, green and blue light-producing phosphors deposited or arranged on the inner surface of the face plate in repeated triades of vertical red, green and blue phosphor stripes in :the manner illustrated exaggeratedly in Figure 1 at R, G, B.

Formed over the screen 7 is an electron permeable conductive layer 8 which may be of aluminum or any other suitable conductive material and constitutes what shall herein-after be referred to as the first electrode in the :target electrode structure 6. Also included in the target electrodeV structure 6 and provided for cooperating with the first electrode 8 is a second electrode in the form of a grille generally designated 10. The grille 10 comprises a plurality of closely spaced Wires 11 extending substantially parallel to each other and to the stripes of phosphorescent material comprising the screen 7. The size and spacing of the grille wires 11 are also illustrated exaggeratedly in the drawing.

By means not shown the second electrode 1'0 is supported for conforming substantially to the curvature of the face plate 4 so as to provide substantially uniform spacing between the first and second electrodes 8 and 10, respectively, across the target electrode. In the justdescribed target electrode structure the first electrode 8 is adapted for being maintained at a potential higher than that of the second electrode 10, thereby to set up and maintain a predetermined electric field in the inter-electrode region defined by the electrodes. By virtue of its construction, the second electrode 10 is permeable to charged particles or electrons directed toward the screen. Thus, during the operation of the tube 1, electron beams or beam components directed toward the target electrode by beam producing means, which will be described hereinafter, are admitted into the inter-electrode region through the spaces between the wires y11 and travel through this region for striking or impinging upon the phosphorescent material screen 7. In the inter-electrode region the higher potential of the conductive layer or rst electrode 7 is effective for attracting and thereby accelerating the movement of the electrons comprising the beam components toward the screen -thereby to increase the striking force of the electrons on the screen whereby color brightness is increased. Additionally, the second electrode serves properly lto focus lthe electron .beam components entering the Yinter-electrode region and to:

directthem-onto the phosphor stripes in'a predetermined desired manner.

Provided for producing the electron beams or beam components for im'pinging on the screen and located i-n the neck portion 3 ofthe tube envelope is a plurality of electron beam or vbeam component producing means or guns 12. 'The guns 12 are preferably substantially coplanar or arranged in a substantial planar .array extende ing perpendicular fto the .phosphor lstripes of the screen 7 and .the .wires of the grille 10. Additionally, the guns 12 are equal in number to the number of primary colors -in which an image is yto bereproduced on .the screen 6;.,

.component convergence means whichincludes a pair vof neck of the tube and having the emitting ends ofthe guns 12'extend .therethroughiand .inconductive .connection therewith. Thus, -the lower plates 25a fare adapted for being maintained at `gun potential. The diaphragm 26 is not shown in Figure l for purposes of simplified illusand, therefore, in the illustrated embodiment three guns i.

are provided. Each .of `the guns 12 may be of the conventional type, consisting of a cathode, a control grid, one or more accelerating electrodes and a .focusing electrode, none of which elements need be speciiically illustrated or described. The :three guns 12 are suitably connected through an insulative tube base 13 to a conventional video signal'source generally designated 14; and, in accordance with color intelligence received from .the source 14, the guns 12 produce and direct toward the target electrode 6 schematically represented beam cornponents 15, 16 kand 17 which extend in a substantially coplanar array.

It will be seen that, while I have shown and .described the beam component producing means as constituting a plurality of individual electron gun structures, any means may be employed for producing and directing toward the target electrode Va plurality of beam components which should be understood herein to denote individual electron-beams formed by separatej means or separate portions of a stream of electrons'einanating from a single means. f l

By means of horizontal and vertical deflection coils schematically illustrated and designatedV 20 andv 21, respectively, `the beam components emanating from the guns 12 Vare deflected in both horizontal and vertical planes of deflection thereby to scan a raster at the target electrode 6. The operation of ,the horizontal and vertical deection coils is controlled by conventional horizontal and vertical deflection signal `generators generally designated 22 and 23, respectively, the construction and .operation of which are well-known in the art.

In a tube structure such as that described above, and as seen in Figure l, the guns 12 are physically aligned or aimed in assembly for ideal convergence and crossl over of the beam components 15, 16 and 17 in substantially the same vertical plane as the planev of the grille 10 and for ideal impingement upon the screen 7 in substantially the same horizontal plane where the center component is directed along the longitudinal axis of th tube. i'

However, as a practical matter, and due to diiculties in obtaining satisfactorily accurate gun alignment by known manufacturing and` assembling methods, the d escribed ideal convergence and impingement are not obtained without providing some form of; beam-convergence means or means forinitially or statically converging the beam componentsl in both verticall and horizontal planes to correct for any inaccuracies in physical alignment. That is, withoutr some form of initial or static beamconvergence means the beam componentsl 15, 16. and 17 would tend to impinge upon the screen 6 in different horizontal planesk andthe outer components wouldV tend to follow trajectories resulting in reduced and yunsatisfactory resolution and inA excitt-,ttionl of` other than respective phosphor stripesof particular triads.

In order to obtain the necessary. static convergence on a horizontal-.plane at the screen I havev providedy beam tration. The upper Iplates c'lesigna't'edZSb are mounted on the diaphragm 26 in any suitable manner whereby they are insulated from the diaphragm and electrically isolated Atr'om effects of electric potentials applied` to other components of the tube, as for example, those of the guns 12 'and the target electrode 6.-

. As seen in Figure ,1, yeach pair of -gplates 25-b is adapted for beingsuitably electrically connected to an electrostatic convergence control source generally 'designated 27. For example, electrical connections between the plates 251) 'and :the control source 27 may be'made through lterminal pins (not shown) in the tube base 13. The source 27 'may .be one of any of a number of suitable generally available circuit arrangements and is adapted fori'electrostatically and independently controlling 'each pair of plates 25 thereby to effect any desired amount `of vertical deflection of corresponding ones of the outer beam components. Thus, the two pairs of plates 25 are adapted for effecting static convergence of the outer beam cornponents 15 and `17 on substantially the same horizontal plane at the screen 7 as the center beam component 16- or on any plane of deflection that might be determined ,by the physical alignment of the center gun and the resultant impingement of lthe center beam component.

It is also necessary to effect static convergence of the youter beam componnents 15 and 17 on the inner lbeam component 16 in a horizontal plane-in the manner illustrated by solid lines 15, 16, 17 in Figure l, thereby to provide for cross-over of the beams in the plane of the grille 10 and satisfactory impingement of phosphor stripes at desired points or atsubstantially the central portions thereof. The static convergence in-'the horizontal plane is accomplished 4by magnetic deection and to this end the pairs of plates 25 are formed of any suitable soft-magnetic material or any material which has high magnetic permeability and low magnetic retentivity, such as soft iron. The plates 25 are thus adapted for serving as internal pole pieces in the static magnetic convergence arrangement including externally disposed magnetic field producing means.

As. seen in- Figure 2 eachof the. plates 25a and 25b associated pair of plates 25. Each of the electromagnets 30 includes a substantially U-'shaped soft-magnetic mate'rial core 31 which may be formed of ferrite or the like. 'Ihe core 31 is adapted` for carrying a coil or winding '32 on the center portion thereof. The coil 32 is utilized in the static convergence control of the beam components and will hereinafter be referred to as the static magnetic coil., Additionally, as shown in Figure 2, the core 31 includes.- upper andA lower legl portions 33 and 34, respectively, the ends ofl which constitute externall magnetic pole pieces which are shaped for conformi-ng substantially to the externalsurface ofthe tube: neck and are disposed 5 for' cooperating na'getically with a corresponding pair of the plates 25 to establish magnet iields between pairs of vertically spaced plates 2S. The conformance of the ends of the core leg portions 33 and 34 and the arcuate portions 28 of the internal pole pieces 25a. and 25b afford the establishment of fields or greater strength between the pole pieces for a .given energizing current. 'The upper and lower leg portions of the core 31` carry coils 35 and 36, respectively. The coils 35 and 36 are adapted for utilization in la dynamic convergence control arrangeinent the purpose, structure and function of which will be ybrought out in detail hereinafter; and the coils 35 and 36 will -be referred to as the dynamic magnetic coils.

The "static magnetic coils 32 are each suitably electrically connected to a static electromagnetic convergence control source generally designated 37 in Figure l. The

source 37 may be any suitable arrangement adapted for unidrec-tionally energizing each of the electromagnets 30 through its respective coil 32 and forv energizing the electromagnets in opposite polarity. When the magnets 30 are thus energized magnetic fields at the pole pieces 33 and 3'41are caused to extend through the tube envelopes 'to the elements 25a and 25bfor establishing transverse magnetic fields between each pair 25 thereof, whereby the outer beams 15 and 17 are caused to shift inwardly land converge on the inner beam 16. The static electromagnetic convergence control source 37 is adjustably controllable so that the convergence of each outer component -is such as to provide for cross-over in the plane of the grille 11. Thus, the beam components are statically electnomagnetically converged for impinging respective phosphor stripes of an individual triad of stripes in the desired manner.

It will be understood that in effecting this initial or static convergence of the beam components, the components may be in any desired one of their different deeeted positions. For example, they may be initially converged at the center of the raster to be scanned in the manner illustrated in solid lines in Figure 1. Alternatively they may be initially converged at any corner of the raster` It will be understood further that while I have illustrated and described electromagnetic means for static magnetic Lbeam component convergence other magnetic means such as arrangements including permanent mag nets located either internally or externally of the tube envelope may be alternatively employed as the magnetic ield producing means. Furthermore, if desired, the plates 25a and 25b serving as the internal pole pieces may each be formed of suitable material for being permanently magnetized predetermined degrees: to provide .for predetermined magnetic deflection of the components.

As seen in Figure l, the screen 7 is arcuate in the horizontal plane. It is similarly 'arcuate in a vertical plane. Thus, it will be seen that in scannin-g of the beam components, the trajectory of each component impinging upon the screen will vary in length in accordance with the raster position. In the vicinity of the axis of the tube and difference between. the lengths of components is: negligible but such differences increase progressively outwardly from the tube axis and the static convergence obtained in the above-described manner becomes progressively less effective as the components scan outwardly.

The diiferences in lengths of the component trajectories has no appreciable effect on the convergence obtained electrostatically, or the relative vertical points of impingement on the screen 7, since the component sources or electron guns 12 are cop-lanar. However, the differences in lengths of the trajectories at various raster positions results in undesired variations in horizontal convergence and color impurities. Thus, dynamic convergence means is required in order to obtain desired horizontal beam component convergence at all raster positions. In the present embodiment I have provided a dynamic convergence arrangement which includes the above-mentioned dynamic magnetic coils 35 and 36 and operates im accordance with predetermined functions of the delietion of the components. f Y

' The coils 35yare oppositely wound and suitably eleci trically connected to a horizontal dynamic convergence signal generator 40 whichmay be of any suitable conventional type adapted for generating signals of a sinusoidal wave form having clipped upper crests. The signal generator 40 is coupled to the horizontal deflection signal generator 22. Thus, in accordance with the function of the horizontal deection signal generator '22, the convergence signal generator 40 is adapted for generating a wave form effective for so energizing the coils 35 as to affect predetermined variationsin the strengths of the fields produced thereby between the pairs of plates or in- -ternal pole pieces 25. These eld lstrength variations effeet corresponding variations in thegpaths or trajectories of the outer electron beam components 15 and 17 relative to the longitudinal axis of the tube and the inner or center component 16 as the beam components are traced horizontally across the target electrode. In this manner suitable variations in accordance with the horizontal deflection of the beam components are made in the horizontal convergence angles of the outer components as a step toward producing the desired horizontal convergence of the beam components substantially in the plane of the grille 10 at all points of the raster.

The mentioned desired horizontal convergence at all points of the raster is fully obtained when the paths or trajectories of the outer beam components 15 and 17 are also suitably varied in accordance with the vertical deflection of the beam components. This type of variation is accomplished through the agency of the coils 36. The coils 36 are also oppositely wound and are suitably electrically connected to a vertical dynamic convergence sig nal generator 41. The generator 41 may be of any suitable conventional type adapted for generating signals of parabolic wave forms and is suitably coupled to the vertical deection signal generator 23. By this arrangement and in accordance with the function of the vertical deiiection signal generator 23 there is impressed on the coils 36 a signal which is effective for so varying the strengths of the magnetic fields between the pairs of internal pole pieces 25 as suitably to vary the pre-deflection paths of the outer beam components 15 and 17 in accordance with the vertical detlection thereof.

It will be seen that, while the static magnetic convergence means, the dynamic magnetic convergence means operating in accordance with horizontal component deflection and the dynamic magnetic convergence means operating in accordance With vertical component detiection have each been described separately for the purpose of elucidation, these means function or operate concurrently for determining the strengths of the tields existing between the pairs of pole pieces 25 at any particular time or raster position of the beam components and together cooperate to provide the desired horizontal convergence of the components at each raster position.

It will be seen that while I have illustrated and described the elements 25 as plates, these elements may have any suitable configuration. For example, the opposed surfaces of each pair of plates may be parallel as shown to serve best in the electrostatic convergence of the beam ycomponents while the remaining portions may have any suitable configuration for best concentrating the magnetic lields established therebetween for the dynamic convergence operation above-described.

While I have shown and described a specific embodiment of my invention I do not desire my invention to be limited to the particular form shown and described and I intend by the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A cathode ray tube comprising an envelope, a target electrode, means for directing toward said target electrode a plurality `oi electron beam components one of which constitutes a reference beam component, means `including a pairof `rr'iagnejtic pole pieces-'straddlingat fleast the others of said beam 'components and forming in the ipath thereof magnetic deflection elds,"means for supplying different potentials to the pole pieces of each pair of said pole pieces to form therebetween lan :electrostatic deflection field, whereby said electrostatic and magnetic fields provide predetermined#deflections of 'each of .said other` beam components in niutuallly :perpendicular directions and relative to said reference beam component.

2. lA'cathode ray 'tube comprising an envelope, la. target electrode, means for directing sever-al substantially Vcio'- planar electron bea-m components towardl said 'target fe'lectrode, a pair of magnetic pole pieces associated with each of outer ones of said beam components 'in said envelope,

v said pole pieces being adapted 'for magnetic convergence of said outer beam components 'on' a plane determined by an 'inner one of said beam components, and means for supplying a potential difference between each pair of said pole pieces to 'form therebetween an. electrostatic field lfor electrostatic lconvergence of said outer beam components on said inner beam component in :said piane determined by said inner beam component.

3. A cathode -ray tube 'comprising an envelope, a Atarget electrode, a plurality of electron "beam producing means adapted for directing beams tow-ard vsaid 'target 'electrodes, a pair of plates =o`f soft-magnetic-material Yforming magnetic pole pieces straddling one of said beams yand 'insulated from said beam producing means, means for supplying a lpotential difference between 'said pole pieces to form therebetween an electrostatic `iield, electrostatic convergence of 'said one beam on a plane determined 'by another of said beams, andisaid pole pieces being adapted for having a magnetic field established therebetween A"for magnetic convergence of vsaid one vbeam on said other beam `in said plane determined by Vsaid other beam.

4."In combination -a cathode ray tube 'including an envelope, a target electr-ode, means for directing toward said ltarget ielectrode a plurality of electron beam vcornponents one oi which yconstitutes a reference beam component, means for deiiecting `said beam :components .to scan a raster at said target electrode, electrostatic detiection means the path of at least 'the other ones vof said beam components for deecting said other beam .cornponents in one direction, saidfelectrostatic deflection means including common magnetic ipole'piec'es'ior deecting said other beam vcomponents `in la direction 'perpendicular to said -ono direction.

5. In 'combination aca'thode ray'tube 'including an envelope, a target electrode, means for directing several electron 'beam components toward .said target electrode, means for vdeiiccting saidbearn components to scarta raster at said target electrode, means `adapted 4for electrostatically converging outer ones lof said beam 'coms -i i ponents on a zplane Adete'rnztined byan inner one ,of beam "components, means adapted for eiectingstatic magnetic `convergencefoi said outer beam components on said inner beam "componerrtkin said plane and adapted for: eiiecting 'dynamic magnetic convergence said Vouter beam components onV said innerbeamcomi portent-in `said plane in accordance with the raster rposition thereof.`

6. In `combinationa cathod ray tube including an envelope, a tanget electrode, means for direc-ting several s ibstan'tial'ly -coplanar electronbeam components toward said target electrode, means for deilecting said Vbeam come ponen-ts to scana raster at said target electrode, va pai-r of Asoft-rrnagnetic material elements straddl-ing each of the Quter'ones of saidy beam components in saidenvelopef, said elements being adapted for effecting electrostatic convergence of said outcrfb'eam cor-ripofnentsl on. a plane determined by an inner one of said beam components, magnetic field producing means disposed externally 'of said envelope and-adapted for establishing magneticgiields between said elements, said field producing means being energizable to establish magnetic elds between said ele.h ments eiiectivefforl magnetically converging-said outer beam components in said plane determined by said inner beam component.v

7-. in combination -a cathode ray tube including' an envelope, al target electrode, several substantially planar beam producing means adapted for directing electron beams towardv said target electrode, means for deiiecting said beams to scan a raster at .said target electrode, a pair of sofbmagnetic-material elements straddl-ing each of the outer ones of said beams in said envelope and. insulated from said beam producing means, said elements being adapted for eectingy electrostatic convergence of saidouter beams on av plane determined by anv inner one of said beams, magnetic ield producing means disposed externally of said envelope and adapted for 4'establishing magnetic elds between said elements, said ieldr producing means being energizable to establish magnetic fields between said elements effective for both static and dynamic convergence of said outer beams insaid plane determined by said beam. l

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Jones July 31,y 1-956 

